The invention relates to an arrangement for open-end friction spinning with two adjacently arranged rollers driven in the same rotational direction and having cover surface areas which together form a wedge-shaped yarn forming gap. The wedge-shaped gap has a narrowing area serving as the yarn formation region. A fiber inlet and opening device supplies fiber material in the form of single separated fibers to the wedge-shaped gap. A yarn withdrawal device is provided for drawing off the produced yarn in the longitudinal direction to the wedge-shaped gap.
With an arrangement of the kind mentioned above disclosed in German Published Unexamined Application (DE-OS) No. 24 49 583, the supplied single fibers are simultaneously pressed against the two cover surface areas of the rollers by means of which they are spun to form a yarn which is drawn off in the longitudinal direction of the wedge-shaped gap. The yarn, simultaneously pressed against the two cover surface areas within the narrowing area of the wedge-shaped gap is retained against the withdrawal force introduced by the yarn withdrawal device by means of the friction force occurring between the produced yarn and these roller cover surface areas. On the one hand it is desired to produce the highest possible tensile forces during the drawing off of the produced yarn since this directly increases the tenacity of the yarn being produced. On the other hand, an increase in the tensile forces increases the danger that yarn end, or so called yarn tip, being formed is irregularly stretched resulting in what has been described as decoupling. These delays or irregularities exhibit themselves as thickened and thinned portions along the length of the produced yarn.
Futhermore, it is quite frequently discovered that an increased twisting is observed in the thinned sections within the yarn.
With another arrangement disclosed in German Published Unexamined Application (DE-OS) No. 28 10 184, the yarn formation does not occur in the narrowed area of the wedge-shaped gap, but within the area of the smallest distance between the cover surface areas of the two rollers. It has been contemplated with such an arrangement to provide these cover surface areas with elevations in such a manner that the wedge-shaped gap extends in the area of its narrowest portion in a wavy line, while said cover surface areas jointly comb the yarn without touching each other. With this arrangement, where the yarn to be produced is not simultaneously pressed together through the cover surface areas of the two rollers, the construction of the wedge-shaped gap as being wave-like in shape is to prevent that the open yarn end being produced does not move back and forth during yarn formation.
It is an object of this invention to provide an arrangement of the above-mentioned kind which makes it possible to work with a higher tensioning force within the yarn end that is being produced while at the same time the danger of stretching or decoupling within the yarn being produced is decreased.
This object is achieved according to the invention by providing that the cover surface area of at least one of the friction rollers is designed to provide for sequential zones in the region of yarn formation in the direction of the yarn withdrawal, in which zones different radial forces and/or different rotational speeds act upon the yarn being produced.
It was established that by these measures, the yarn being produced can be spun with a surprisingly higher tensioning withdrawal force, while at the same time the danger with respect to occurrences of thinning/thickening portions is decreased. Furthermore, an increased twisting is not produced in the thinning portions that occassionally occur.
In a preferred embodiment of the invention, it is provided that the cover surface area of at least one of the rollers is provided with zones in the area of the mouth of a fiber feed channel. These zones are then provided only in those areas in which fibers are still to be spun in the yarn being produced.
In another embodiment of the invention, the cover surface area of at least one of the rollers includes one or more circumferential grooves. These grooves permit the change of the axial compression of the produced yarn and the transfer of twist by means of different rotational speeds whereby at the same time the tension force can be increased.
Further objects, features, and advantages of the present invention will become more apparent from the following description when taken with the accompanying drawings which show, for purposes of illustration only, several embodiments in accordance with the present invention.